1. Field of the Invention
The present invention relates to a fastening member for fastening a decorative external panel to a front surface of an underlying panel disposed in front of a construction frame of a building, and an external wall construction structure using the fastening member.
2. Description of the Related Art
Conventionally, there exists an external wall construction structure in which fastening members are fastened to underlying panels disposed in front of a construction frame of a building and a plurality of external wall panels are engaged with the fastening members (see, e.g., Japanese Unexamined Laid-open Patent Publication No. 2005-133504).
Furthermore, as shown in FIG. 14, there also exists an external wall construction structure 97 in which decorative external panels 96 are disposed in front of underlying panels 95 disposed in front of a construction frame 93.
This external wall construction structure 97 includes an underlying panel 95 disposed in front of a construction frame 93, a fastening member 91 fastened to the front surface of the underlying panel 95, and a decorative external panel 96 engaged with the fastening member 91.
The fastening member 91 has a base plate portion 910 and a supporting portion 913, and is fastened to the underlying panel 95 with a screw 92 inserted in a screw hole 920 formed in the base plate portion 910.
In the aforementioned external wall construction structure 97, since various functions required for external wall construction structure, such as, e.g., waterproofing, can be given to the underlying panel 95, the decorative external panel 96 can be specialized in achieving an ornamental function. Consequently, the weight of the decorative external panel 96 can be reduced, thereby enabling the use of a thin and low-cost fastening member 91.
In cases where a screw 92 is inserted into the fastening member 91 located at a vertical position approximately the same vertical position of the end portion 950 of the underlying panel 95, the screw 92 will be screwed into the end portion 950 of the underlying panel 95 which is relatively weak in strength, which may cause cracking and/or breaking of the end portion 950. As a result, this could lead to difficulty in obtaining external wall construction structure 97 having sufficient strength.
On the other hand, in order to secure a sufficient distance between the end portion 950 and a screw hole 920 of the fastening member 91, it can be considered to configure the fastening member 91 such that a plurality of screw holes 920 are arranged at intervals along the vertical (up-and-down) direction so that a screw 92 can be inserted into a screw hole 920 farther away from the end portion 950.
In this case, however, since the vertical length of the base plate portion 910 becomes longer, the fastening of the base plate portion 910 with a screw 92 using a screw hole 920 farther away from the supporting portion 913 results in an increased distance between the screw hole 920, serving as a fulcrum and the supporting portion 913, serving as a working point. This may cause a deformation of the base plate portion 910 when bending stress acts on the base plate portion 910.
Especially, since the fastening member 91 is formed into a thin member as mentioned above, the base plate portion 910 is decreased in bending strength. Therefore, supporting the decorative external panel 96 may cause frontward bending of the lower end 912 of the base plate portion 910. This in turn causes an inclination of the decorative external panel 96 to the underlying panel 95, resulting in misaligned decorative surfaces 960 of the decorative external panels 96, which deteriorates the design appearance.